linux-kernel - Re: [PATCHv2] Bluetooth: quirk disabling LE Read Transmit Power

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Date:   Fri, 19 Nov 2021 16:59:32 +0000
From:   Aditya Garg <gargaditya08@...e.com>
To:     Marcel Holtmann <marcel@...tmann.org>
CC:     Orlando Chamberlain <redecorating@...tonmail.com>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        Daniel Winkler <danielwinkler@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Johan Hedberg <johan.hedberg@...el.com>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Luiz Augusto von Dentz <luiz.dentz@...il.com>,
        "regressions@...ts.linux.dev" <regressions@...ts.linux.dev>,
        "sonnysasaka@...omium.org" <sonnysasaka@...omium.org>
Subject: Re: [PATCHv2] Bluetooth: quirk disabling LE Read Transmit Power



> On 18-Nov-2021, at 12:31 AM, Marcel Holtmann <marcel@...tmann.org> wrote:
> 
> Hi Orlando,
> 
>>> So if this just affects two macs, why can't the fix be realized as a
>>> quirk that is only enabled on those two systems? Or are they impossible
>>> to detect clearly via DMI data or something like that?
>> 
>> I think we should be able to quirk based off the acpi _CID "apple-uart-blth"
>> or _HID "BCM2E7C". Marcel suggested quirking based of the acpi table here
>> https://lore.kernel.org/linux-bluetooth/1D2217A9-EA73-4D93-8D0B-5BC2718D4788@holtmann.org/
>> 
>> This would catch some unaffected Macs, but they don't support the LE Read
>> Transmit Power command anyway (the affected macs were released after it
>> was added to the Bluetooth spec, while the unaffected Macs were released
>> before it was added to the spec, and thus don't support it).
>> 
>> I'm not sure how to go about applying a quirk based off this, there are
>> quirks in drivers/bluetooth/hci_bcm.c (no_early_set_baudrate and
>> drive_rts_on_open), but they don't seem to be based off acpi ids.
>> 
>> It might be simpler to make it ignore the Unknown Command error, like
>> in this patch https://lore.kernel.org/linux-bluetooth/CABBYNZLjSfcG_KqTEbL6NOSvHhA5-b1t_S=3FQP4=GwW21kuzg@mail.gmail.com/
>> however that only applies on bluetooth-next and needed the status it
>> checks for to be -56, not 0x01.
> 
> so we abstain from try-and-error sending of commands. The Bluetooth spec
> has a list of supported commands that a host can query for a reason. This
> is really broken behavior of the controller and needs to be pointed out as
> such.
Well all I can do is provide you any logs or information I can. But we do really wish to get this regression fixed soon.
> 
> The question is just how we quirk it.
> 
> Regards
> 
> Marcel
>